761 research outputs found
Tilted two-fluid Bianchi type I models
In this paper we investigate expanding Bianchi type I models with two tilted
fluids with the same linear equation of state, characterized by the equation of
state parameter w. Individually the fluids have non-zero energy fluxes w.r.t.
the symmetry surfaces, but these cancel each other because of the Codazzi
constraint. We prove that when w=0 the model isotropizes to the future. Using
numerical simulations and a linear analysis we also find the asymptotic states
of models with w>0. We find that future isotropization occurs if and only if . The results are compared to similar models investigated previously
where the two fluids have different equation of state parameters.Comment: 14 pages, 3 figure
1-2-3-flavor color superconductivity in compact stars
We suggest a scenario where the three light quark flavors are sequentially
deconfined under increasing pressure in cold asymmetric nuclear matter, e.g.,
as in neutron stars. The basis for our analysis is a chiral quark matter model
of Nambu--Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single
flavor (CSL) and spin-0 two/three flavor (2SC/CFL) channels, and a
Dirac-Brueckner Hartree-Fock (DBHF) approach in the nuclear matter sector. We
find that nucleon dissociation sets in at about the saturation density, n_0,
when the down-quark Fermi sea is populated (d-quark dripline) due to the flavor
asymmetry imposed by beta-equilibrium and charge neutrality. At about 3n_0
u-quarks appear forming a two-flavor color superconducting (2SC) phase, while
the s-quark Fermi sea is populated only at still higher baryon density. The
hybrid star sequence has a maximum mass of 2.1 M_sun. Two- and three-flavor
quark matter phases are found only in gravitationally unstable hybrid star
solutions.Comment: 4 pages, 2 figures, to appear in the proceedings of Quark Matter
2008: 20th International Conference on Ultra-Relativistic Nucleus Nucleus
Collisions (QM 2008), Jaipur, India, 4-10 Feb 200
Late-time behaviour of the Einstein-Vlasov system with Bianchi I symmetry
The late-time behaviour of the Einstein-dust system is well understood for
homogeneous spacetimes. For the case of Bianchi I we have been able to show
that the late-time behaviour of the Einstein-Vlasov system is well approximated
by the Einstein-dust system assuming that one is close to the unique stationary
solution which is the attractor of the Einstein-dust system.Comment: 4 pages, based on a talk given at the Spanish Relativity Meeting
2010, to appear in Journal of Physics: Conference Series (JPCS
Late-time behaviour of the Einstein-Vlasov system with Bianchi I symmetry
The late-time behaviour of the Einstein-dust system is well understood for
homogeneous spacetimes. For the case of Bianchi I we have been able to show
that the late-time behaviour of the Einstein-Vlasov system is well approximated
by the Einstein-dust system assuming that one is close to the unique stationary
solution which is the attractor of the Einstein-dust system.Comment: 4 pages, based on a talk given at the Spanish Relativity Meeting
2010, to appear in Journal of Physics: Conference Series (JPCS
Late-time behaviour of the Einstein-Vlasov system with Bianchi I symmetry
The late-time behaviour of the Einstein-dust system is well understood for
homogeneous spacetimes. For the case of Bianchi I we have been able to show
that the late-time behaviour of the Einstein-Vlasov system is well approximated
by the Einstein-dust system assuming that one is close to the unique stationary
solution which is the attractor of the Einstein-dust system.Comment: 4 pages, based on a talk given at the Spanish Relativity Meeting
2010, to appear in Journal of Physics: Conference Series (JPCS
Perfect fluids and generic spacelike singularities
We present the conformally 1+3 Hubble-normalized field equations together
with the general total source equations, and then specialize to a source that
consists of perfect fluids with general barotropic equations of state.
Motivating, formulating, and assuming certain conjectures, we derive results
about how the properties of fluids (equations of state, momenta, angular
momenta) and generic spacelike singularities affect each other.Comment: Considerable changes have been made in presentation and arguments,
resulting in sharper conclusion
Recent progress constraining the nuclear equation of state from astrophysics and heavy ion reactions
The quest for the nuclear equation of state (EoS) at high densities and/or
extreme isospin is one of the longstanding problems of nuclear physics. Ab
initio calculations for the nuclear many-body problem make predictions for the
density and isospin dependence of the EoS far away from the saturation point of
nuclear matter. On the other hand, in recent years substantial progress has
been mode to constrain the EoS both, from the astrophysical side and from
accelerator based experiments. Heavy ion experiments support a soft EoS at
moderate densities while recent neutron star observations require a ``stiff''
high density behavior. Both constraints are discussed and shown to be in
agreement with the predictions from many-body theory.Comment: Invited talk given at NPA III, Dresden, Germany, March 200
3.9 angstrom structure of the nucleosome core particle determined by phase-plate cryo-EM
The Volta phase plate is a recently developed electron cryo-microscopy (cryo-EM) device that enables contrast enhancement of biological samples. Here we have evaluated the potential of combining phase-plate imaging and single particle analysis to determine the structure of a small protein-DNA complex. To test the method, we made use of a 200 kDa Nucleosome Core Particle (NCP) reconstituted with 601 DNA for which a high-resolution X-ray crystal structure is known. We find that the phase plate provides a significant contrast enhancement that permits individual NCPs and DNA to be clearly identified in amorphous ice. The refined structure from 26,060 particles has an overall resolution of 3.9 angstrom and the density map exhibits structural features consistent with the estimated resolution, including clear density for amino acid side chains and DNA features such as the phosphate backbone. Our results demonstrate that phase-plate cryo-EM promises to become an important method to determine novel near-atomic resolution structures of small and challenging samples, such as nucleosomes in complex with nucleosome-binding factors
WISER Deliverable D3.3-2: The importance of invertebrate spatial and temporal variation for ecological status classification for European lakes
European lakes are affected by many human induced disturbances. In principle, ecological
theories predict that the structure and functioning of benthic invertebrate assemblage (one of
the Biological Quality Elements following the Water Framework Directive, WFD
terminology) change in response to the level of disturbances, making this biological element
suitable for assessing the status and management of lake ecosystems. In practice, to set up
assessment systems based on invertebrates, we need to distiguish community changes that are
related to human pressures from those that are inherent natural variability. This task is
complicated by the fact that invertebrate communities inhabiting the littoral and the profundal
zones of lakes are constrained by different factors and respond unevenly to distinct human
disturbances. For example it is not clear yet how the invertebrates assemblages respond to
watershed and shoreline alterations, nor the relative importance of spatial and temporal
factors on assemblage dynamics and relative bioindicator values of taxa, the habitat
constraints on species traits and other taxonomic and methodological limitations.
The current lack of knowledge of basic features of invertebrate temporal and spatial variations
is limiting the fulfillment of the EU-wide intercalibration of lake ecological quality
assessment systems in Europe, and thus compromising the basis for setting the environmental
objectives as required by the WFD. The aim of this deliverable is to provide a contribution
towards the understanding of basic sources of spatial and temporal variation of lake
invertebrate assemblages. The report is structured around selected case studies, manly
involving the analysis of existing datasets collated within WISER. The case studies come
from different European lake types in the Northern, Central, Alpine and Mediterranean
regions. All chapters have an obvious applied objective and our aim is to provide to those
dealing with WFD implementation at various levels useful information to consider when
designing monitoring programs and / or invertebrate-based classification systems
Core collapse supernovae in the QCD phase diagram
We compare two classes of hybrid equations of state with a hadron-to-quark
matter phase transition in their application to core collapse supernova
simulations. The first one uses the quark bag model and describes the
transition to three-flavor quark matter at low critical densities. The second
one employs a Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model with
parameters describing a phase transition to two-flavor quark matter at higher
critical densities. These models possess a distinctly different temperature
dependence of their transition densities which turns out to be crucial for the
possible appearance of quark matter in supernova cores. During the early post
bounce accretion phase quark matter is found only if the phase transition takes
place at sufficiently low densities as in the study based on the bag model. The
increase critical density with increasing temperature, as obtained for our PNJL
parametrization, prevents the formation of quark matter. The further evolution
of the core collapse supernova as obtained applying the quark bag model leads
to a structural reconfiguration of the central proto-neutron star where, in
addition to a massive pure quark matter core, a strong hydrodynamic shock wave
forms and a second neutrino burst is released during the shock propagation
across the neutrinospheres. We discuss the severe constraints in the freedom of
choice of quark matter models and their parametrization due to the recently
observed 2 solar mass pulsar and their implications for further studies of core
collapse supernovae in the QCD phase diagram.Comment: 19 pages, 4 figures, CPOD2010 conference proceedin
- âŠ